Loads a JavaScript file asynchronously with a callback, like jQuery's $.getScript()
except without jQuery.
function j(u, c) {
var h = document.getElementsByTagName('head')[0], s = document.createElement('script');
s.async = true; s.src = u;
s.onload = s.onreadystatechange = function () {
if (!s.readyState || /loaded|complete/.test(s.readyState)) {
s.onload = s.onreadystatechange = null; if (h && s.parentNode) { h.removeChild(s) } s = undefined;
if (c) { c() }
}
};
h.insertBefore(s, h.firstChild);
}